<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
</head>
<body>
<div id="timer" style="color:red"></div>
	<SCRIPT LANGUAGE="JavaScript">   
<!--   
var maxtime = 60*60 //一个小时，按秒计算，自己调整!   
function CountDown(){   
if(maxtime>=0){

minutes = Math.floor(maxtime/60);   
seconds = Math.floor(maxtime%60); 
minutes = minutes>=10?minutes:'0'+minutes;
seconds = seconds>=10?seconds:'0'+seconds;  
msg = "距离结束还有"+minutes+"分"+seconds+"秒";   
document.all["timer"].innerHTML=msg;   
if(maxtime == 5*60) alert('注意，还有5分钟!');   
--maxtime;   
}   
else{   
clearInterval(timer);   
alert("时间到，结束!");   
}   
}   
timer = setInterval("CountDown()",1000);   
//-->   
</SCRIPT> 
</body>